Be sure to request either the micro;-center mark or the >< center mark. If no pattern is selected, the default pattern will be the one with the micro;-center mark. The filmed coatings will be as described, but note that what we have described as "Silicon Dioxide (SiO2)/Monoxide (SiO)" is the result of an evaporation of SiO (silicon monoxide) at high vacuum and the end result is generally thought to be a combination of SiO2 and SiO. In any case, for nearly all users of this product, what seems to be important is not knowing the precise composition, but knowing that in a plasma etcher, oxygen will not etch or otherwise harm the film.
The case for molybdenum grids:
These grids are used primarily for those doing high temperature studies, which would mean that any polymer, such as Formvar®, would be degraded during the heating. Actually, SPI Supplies features the world's largest and most diverse selection of different molybednum TEM grids, so if you would prefer some other pattern, it too probably could be coated, and either for the same price or just slightly more. Just tell us what you want and we will return with a confirmation of pricing!
For high temperature studies, the SPI Supplies® Brand of Silicon Nitride Membrane Window Grids might be a better choice since one can do in situ heating experiments beyond 1000° C without the membrane rupturing.
And if you are someone wanting to use a 50 mesh grid, which would suggest you would want to have the largest possible grid square area, the SPI Supplies® Brand of Silicon Nitride Membrane Window Grids could also be attractive for that reason as well. In that case, the "window" can be as large as 1 mm square and withot the problem of "grid sag", that is, the sag of the carbon or other support film across a hole as large as would be present in a 50 mesh grid. Remember also that a hole that large will have associated with it some amount of image drift as well as great uncertainties in the magnification (because of the already mentioned problem of grid sag).
Perforated support films:
We do offer not only holey carbon and lacey carbon coated grids, we also offer them as carbon/Formvar holey and carbon/Formvar lacey and for some applications, the latter are the more desirable. Of course if samples are being deposited from solvents, which could dissolve the Formvar, the grids with Formvar would not be recommended.
There are other options for perforated support systems. Many users worldwide, especially for electron tomography applications prefer the Quantifoil® Micromachined Holey Carbon Grids which offer certain advantages.
The newest option is the use of the SPI Supplies® Brand Perforated Silicon Nitride Membrane Window Grids. There might be some "sticker shock" here, as these grids are much more expensive than the more conventional grids, but they do permit certain types of work that can be done better (or not at all) some other way. For example, for cryo TEM studies on liquids, these grids are beyond compare. They are also the ultimate support grid for FIB lift-off samples. These are the only grids that one can perform, on the very same field of observation, AFM, FESEM and also TEM.